We found that adult mosquito females challenged with Plasmodium respond more efficiently to subsequent challenges. This effect is long lasting and both the priming and the recall require ookinete invasion of midgut epithelial cells in the presence of bacteria from the midgut flora. The priming response involves hemocyte differentiation that results in a long-lasting increase in the number of circulating granulocytes, the major cells involved in phagocytosis. We found that this response is enhanced in mosquitoes previously exposed to Plasmodium infection. Furthermore, the transfer of cell-free hemolymph from challenged mosquitoes to newly emerged sugar-fed females induces hemocyte differentiation and confers increased resistance to Plasmodium infection. Our studies indicate that hemocyte differentiation mediates innate immune memory in mosquitoes. We characterized the Immunomodulatory Peroxidase (IMPer), an enzyme secreted by the mosquito Anopheles gambiae midgut in response to blood feeding, and dual oxidase (Duox) form a dityrosine network that decreases gut permeability to immune elicitors and protects the microbiota by preventing activation of epithelial immunity. This network provides a permissive environment for Plasmodium development, as it prevents activation of anti-malarial responses mediated by nitric oxide synthase (NOS). When the formation of this barrier is prevented, by silencing either IMPer or Duox, mosquitoes mount strong pathogen-specific responses to bacteria and Plasmodium. We identified an epithelial serine protease (ESP) that is required for Plasmodium parasites to efficiently invade midgut epithelial cells. Midgut invasion by ookinetes and sporozoite invasion of the salivary gland induces SP30 expression. Furthermore, SP30 silencing significantly decreases the number of parasites that invade these organs. ESP protein is localized in the submicrovillar region of midgut cells and the basal side of salivary gland epithelial cells, the surfaces that parasites interact with during invasion. In the midgut, ESP silencing prevents the induction of Gelsolin, a protein involved in modulating the actin cytoskeleton that is known to also be required for midgut invasion. We found that the midgut epithelial nitration mediated by a heme peroxidase (HPX2) and the NADPH oxidase (NOX5) is an important antiplasmodial effect. The HPX2/NOX5 system potentiates NO toxicity and labels ookinetes as they traverse the midgut, making the visible to the mosquito complement system. We found that there are broad differences in the midgut epithelial responses to Plasmodium invasion between An. gambiae strains. In the G3 strain of An. gambiae Apolipophorin-III (AgApoLp-III) participates in midgut epithelial defense responses that limit Plasmodium infection, while this gene has been reported to have no effect on infection in the An. gambiae (Yaound strain). Our studies also revealed that a An. gambiae strain selected to be refractory (R) to Plasmodium infection has reduced longevity, faster utilization of lipid reserves, impaired mitochondrial state-3 respiration, increased rate of mitochondrial electron leak and higher expression levels of several glycolytic enzyme genes. Furthermore, when state-3 respiration was reduced in Plasmodium susceptible (S) females by silencing expression of the adenine nucleotide translocator, hydrogen peroxide generation was higher and the mRNA levels of lactate dehydrogenase increased in the midgut, while the prevalence and intensity of Plasmodium berghei infection were significantly reduced. We conclude that there are broad metabolic differences between R and S An. gambiae mosquitoes that influence their susceptibility to Plasmodium infection. We identified a QTL in Chr. 13 that confers an African strain of Plasmodium falciparum (GB4) the ability to survive in An. gambiae (L35) females. In contrast, 98-100% of P. falciparum 7G8 parasites (Brazilian strain) are detected by the mosquito immune system and killed. The QTL encompasses a 171.8 kb region coding for 42 genes. We confirmed that QTL regions using linkage group selection, identified multiple polymorphisms and differences in gene expression. We have identify several potential candidate genes with non-synonymous substitutions or marked differences in gene expression and a screening is underway to identify genes that reverse the genetic phenotypes when expressed episomally.